Photoluminescent Sheet

ABSTRACT

A photoluminescent sheet is disclosed. A photoluminescent sheet that includes a matrix resin layer, which is a thermosetting resin; a phosphor, which is included in the matrix resin layer and which converts the wavelength of light emitted from a blue LED; a curing agent, which is included in the matrix resin layer and which cures liquid thermosetting resin; and an additive, which is included in the matrix resin layer and which disperses the phosphor uniformly within the matrix resin layer, can implement white light from light having wavelengths corresponding to blue color.

TECHNICAL FIELD

The present invention relates to a photoluminescent sheet, moreparticularly, to a photoluminescent sheet capable of implementing whitelight from the blue light of an LED (light emitting diode).

BACKGROUND ART

Various types of lighting equipment are used for providing light in thenighttime or in an indoor space and for spotlighting objects. Suchlighting equipment provides light by receiving electrical energy from anelectrical power source and converting it to light energy, whereincandescent light bulbs or fluorescent tubes are generally used.However, incandescent light bulbs and fluorescent tubes entail highpower consumption and heat emission, and due to their short durabilityof about six months, there is a need for frequent replacement.

In addition, fluorescent tubes use mercury, which is a carcinogenicsubstance, and may thus be subject to regulations, and when fluorescenttubes are used for direct lighting, the flickering of the light sourcemay cause weakened eyesight. There are also several other drawbacks,including the requirement of large installation spaces, and difficultiesin installation and color adjustment, etc.

As an alternative to such conventional lighting devices, much researchhas been focused on lighting devices using LED's (light emittingdiodes). An LED has a semi-permanent durability of about one hundredthousand hours, and since it uses light having a longer wavelength thanthat of ultraviolet rays, it is harmless to the human body.

LED's can be grouped, according to the wavelength of the light emitted,into blue LED's, white LED's, and ultraviolet LED's, etc. However,ultraviolet LED's and white LED's not only require complicatedfabricating processes, but also incur much higher fabricating costs,such that their use is substantially limited. Thus, there is beingdeveloped a photoluminescent sheet for implementing white colors withinexpensive blue LED's. Such lighting equipment may be used for abacklight unit in a cell phone, etc.

However, since the conventional photoluminescent sheet is formed bykneading an inorganic phosphor with a thermoplastic resin as the matrixresin using a two-axis extruder, it is difficult to obtain uniformmixing of the phosphor in the resin sheet, which causes severenon-uniformity in luminance and color coordinates.

Also, since the conventional color conversion sheet was fabricated byextrusion molding a colored pellet, in which a matrix resin and aphosphor were kneaded, identical extrusion-molding conditions producedonly identical forms of color conversion sheet, to result in lowapplicability.

Furthermore, thermoplastic resins such as polycarbonate orpolymethylmethacrylate resin, etc., used for the matrix resin werelimited in application, because they are high in brittleness and mayeasily break, as in the photograph of FIG. 1, and because they are lowin heat-resistance (120° C. or lower) and may easily undergo plasticdeformation at high temperatures.

DISCLOSURE OF INVENTION Technical Problem

An aspect of the present invention aims to provide a photoluminescentsheet which can implement white light using inexpensive blue LED's, andwhich has high resistance to heat, brittleness, and humidity.

Another aspect of the invention aims to provide a photoluminescent sheetin which the surface of the photoluminescent sheet is deformed for lightdiffusion, and in which wetting, which occurs due to contact whenstacking with other sheets, is prevented.

Technical Solution

One aspect of the invention provides a photoluminescent sheet thatincludes a matrix resin layer, which is a thermosetting resin; aphosphor, which is included in the matrix resin layer and which convertsthe wavelength of light emitted from a blue LED; a curing agent, whichis included in the matrix resin layer and which cures liquidthermosetting resin; and an additive, which is included in the matrixresin layer and which disperses the phosphor uniformly within the matrixresin layer.

The photoluminescent sheet may be fabricated, according to usage, as aluminance-enhancing photoluminescent sheet, luminance- andchromaticity-enhancing photoluminescent sheet, or achromaticity-enhancing photoluminescent sheet. These may be fabricatedin the following composition ratios.

When a diffusing agent is not included, a luminance-enhancingphotoluminescent sheet may be fabricated to include 0.05˜5 parts byweight of the curing agent, 0.1˜15 parts by weight of the additive, and1˜90 parts by weight of the yellow phosphor, per 100 parts by weight ofthe silicone resin;

or a luminance- and chromaticity-enhancing photoluminescent sheet may befabricated to include 0.05˜5 parts by weight of the curing agent, 0.1˜15parts by weight of the additive, 1˜30 parts by weight of the greenphosphor, 0.1˜60 parts by weight of the yellow phosphor, and 1˜30 partsby weight of the red phosphor, per 100 parts by weight of the siliconeresin.

Also, a chromaticity-enhancing photoluminescent sheet may be fabricatedto include 0.05˜5 parts by weight of the curing agent, 0.1˜15 parts byweight of the additive, 1˜65 parts by weight of the green phosphor, and1˜65 parts by weight of the red phosphor, per 100 parts by weight of thesilicone resin.

Meanwhile, a diffusing agent may be added to the photoluminescent sheet,where the diffusing agent facilitates the refraction of light from thelight source to increase the excitation rate of the phosphor and make itmore uniform. Such a photoluminescent sheet may have the followingcomposition ratios for various uses.

A luminance-enhancing photoluminescent sheet may be fabricated toinclude 0.05˜5 parts by weight of the curing agent, 0.1˜15 parts byweight of the additive, 5˜15 parts by weight of the diffusing agent, and1˜90 parts by weight of the yellow phosphor, per 100 parts by weight ofthe silicone resin;

or a luminance- and chromaticity-enhancing photoluminescent sheet may befabricated to include 0.05˜5 parts by weight of the curing agent, 0.1˜15parts by weight of the additive, 5˜15 parts by weight of the diffusingagent, 1˜30 parts by weight of the green phosphor, 0.1˜60 parts byweight of the yellow phosphor, and 1˜30 parts by weight of the redphosphor, per 100 parts by weight of the silicone resin.

Also, a chromaticity-enhancing photoluminescent sheet may be fabricatedto include 0.05˜5 parts by weight of the curing agent, 0.1˜15 parts byweight of the additive, 5˜15 parts by weight of the diffusing agent,1˜50 parts by weight of the green phosphor, and 1˜50 parts by weight ofthe red phosphor, per 100 parts by weight of the silicone resin.

Meanwhile, a protective film may be attached to a surface of the matrixresin layer. The protective film is a transparent layer, which protectsthe matrix resin layer for increased resistance to heat and humidity.

The surface of the protective film may have uneven levels. This is forthe functions of diffusion and anti-wetting. Minute balls for preventingwetting may be attached to the surface of the protective film, toprevent wetting when another sheet is placed in contact with thephotoluminescent sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of a photoluminescent sheet according to priorart.

FIG. 2 is a cross-sectional view of a photoluminescent sheet accordingto a first disclosed embodiment of the present invention.

FIG. 3 is a photoluminescent spectra graph of three types ofphotoluminescent sheets according to a second disclosed embodiment ofthe present invention.

FIG. 4 is a graph illustrating the relation between diffusing agentconcentration and luminance in a photoluminescent sheet according to athird disclosed embodiment of the present invention.

FIG. 5 is a flowchart illustrating a method of fabricating aphotoluminescent sheet according to a fourth disclosed embodiment of thepresent invention.

FIG. 6 is a schematic diagram illustrating a method of fabricating aphotoluminescent sheet according to a fourth disclosed embodiment of thepresent invention.

FIG. 7 is a photograph of a photoluminescent sheet according to a fourthdisclosed embodiment of the present invention.

FIG. 8 is a photograph for reliability testing for a photoluminescentsheet according to prior art.

FIG. 9 is a photograph for reliability testing for a photoluminescentsheet according to a fourth disclosed embodiment of the presentinvention.

FIG. 10 is a cross-sectional view of a photoluminescent sheet accordingto a fifth disclosed embodiment of the present invention.

FIG. 11 is a photograph of a photoluminescent sheet having minute ballsattached, according to a fifth disclosed embodiment of the presentinvention.

FIG. 12 is a cross-sectional view of a photoluminescent sheet accordingto a sixth disclosed embodiment of the present invention.

FIG. 13 is a cross-sectional view of a photoluminescent sheet accordingto a seventh disclosed embodiment of the present invention.

DESCRIPTION OF REFERENCE NUMERALS FOR KEY COMPONENTS

-   -   1 a: yellow phosphor    -   1 b: red phosphor    -   1 c: green phosphor    -   1: phosphor    -   2: matrix resin layer    -   3: diffusing agent    -   4: protective film    -   5: minute ball    -   10: photoluminescent sheet    -   20: silicone liquid

MODE FOR THE INVENTION

Embodiments of the invention will be described below in more detail,with reference to the accompanying drawings, where the same referencenumerals are used for the same or corresponding components, andredundant descriptions are omitted.

FIG. 2 is a cross-sectional view of a photoluminescent sheet accordingto a first disclosed embodiment of the present invention. In FIG. 2 areillustrated a yellow phosphor 1 a, red phosphor 1 b, green phosphor 1 c,phosphor 1, matrix resin layer 2, diffusing agent 3, protective film 4,and photoluminescent sheet 10.

The photoluminescent sheet 10 shown in FIG. 2 has the function oftransforming the light of a blue LED, having a wavelength of 400 nm˜500nm, into white light. Basically, it has the form of a thin matrix resinlayer 2 having a phosphor dispersed within.

Although it is not shown in FIG. 2, a curing agent and an additive maybe included inside the matrix resin layer 2. The curing agent is usedfor curing liquid thermosetting resin, and the additive is used fordispersing the phosphor uniformly within the liquid thermosetting resin.The diffusing agent 3 is for increasing the excitation rate of thephosphor and making it more uniform. The protective film 4 is forprotecting the matrix resin layer 2.

The materials used in certain embodiments of the invention are describedas follows.

Matrix Resin Layer 2

In embodiments of the invention, the matrix resin layer 2 is composed ofa thermosetting resin, which may be a silicone resin. Whilethermoplastic resin is easy to handle, it is high in brittleness and lowin humidity-resistance, making it difficult to use in a photoluminescentsheet 10. Thus, in embodiments of the invention, thermosetting resin isused, which involves more complicated processes.

Silicone resin has good flexibility, and has superior adhesion whenprinted on a film. Desirable properties for silicone resin applicable toan embodiment of the invention include a light transmittance of 85% orhigher, a viscosity of 3000 cP or higher, and a drying (curing)temperature of 120° C. or lower. Also, adequate mixing with the phosphor1, etc., may be preferable, as well as low volatility and good adhesionwith the protective film 4. Such silicone resin is commerciallyavailable, for example, the silicone resin system of LS4326 (siliconeresin)—LS4326A (curing agent)—LS4326C (curing accelerator)—toluene orxylene (70%, viscosity controller or solvent), or the silicone resinsystem of CF5010 (silicone resin)—SO400 (curing agent)—silicone oil(viscosity controller or solvent), etc., from Dow Corning Corporation.

Since such silicone resin generally has an antifoaming agent alreadyadded, the problem of bubbling, which may occur in screenprintingapplications, can be resolved. Thus, the silicone resin generallyreferred to below may be regarded not so much as pure silicone resin,but as silicone resin containing small amounts of materials forimproving the properties of the silicone resin. This is because it isdifficult to obtain pure silicone resin in the market, and becausesilicone resin generally referred to by those skilled in the art is thekind sold by silicone resin manufacturers.

Phosphor 1 and Diffusing Agent 3

Materials mixed into the silicone resin for light excitation and/ordiffusion are as follows.

An inorganic phosphor is used for the phosphor 1. A typicallight-excitation inorganic phosphor is composed by doping Y₃A_(l5)O₁₂(YAG) with cerium, where Y₃A_(l5)O₁₂ (YAG) is a material of the garnetgroup. For example, the light-excitation inorganic phosphor may be(Y1-x-yGdxCey)3Al₅O₁₂ (YAG:Gd,Ce), (Y1-xCex)₃Al₅O₁₂ (YAG:Ce),(Y1-xCex)₃(Al1-yGay)₅O₁₂(YAG:Ga,Ce),(Y1-x-yGdxCey)₃(Al5-zGaz)₅O₁₂(YAG:Gd,Ga,Ce), or (Gd1-xCex)SC₂Al₃O₁₂(GSAG), etc.

In general, a YAG-based phosphor is represented as(Y1-x-yGdxCey)₃(Al1-zGaz)O₁₂ (where x+y≦1; 0≦x≦1; 0≦y≦1; 0≦z≦1). Themain wavelengths of the light emitted by the phosphor 1 vary accordingto the material set forth above. Ce³⁺ light emission from a garnetcomposition can provide a variety of colors from green (˜540 nm;YAG:Ga,Ce) to red (˜600 nm; YAG:Gd,Ce), without losses in lightefficiency. In an embodiment of the invention, (Y, Gd, Ce)₃(Al, Ga)₅O₁₂from Daejoo Electronic Materials Co. Ltd., and Y₃Al₅O₁₂:Ce from PhosphorTechnology, Ltd., were used. Also, a typical inorganic phosphor foremitting dark red light is SrB4O7:Sm²⁺. SM²⁺ mainly contributes toproducing wavelengths of a red color. This dark red inorganic phosphorin particular absorbs radiation from the entire visible light range of600 nm or lower, and emits radiation having wavelengths of 650 nm orhigher. For improved luminance, a SrS:Eu based phosphor of wavelengthsaround 620 nm from Phosphor Technology, Ltd., is used. Also, a typicalinorganic phosphor for emitting green light is SrGa₂S₄:Eu²⁺. This greeninorganic phosphor absorbs light of 500 nm or lower, and emits radiationhaving a main wavelength of 535 nm. Also, a typical inorganic phosphorfor emitting blue light is BaMg₂Al₁₆O₂₇:Eu²⁺. This blue inorganicphosphor absorbs light of 430 nm or lower, and emits radiation having amain wavelength of 450 nm.

The yellow phosphor does not necessarily have to be YAG-based, and anyone of TAG-based (Tb₃Al₅O₁₂) or Silicate-based (Sr₂SiO₄:Eu) phosphorsmay also be used. Further, the red phosphor may also be selected fromamong CaS:Eu, SrS:Eu, and SrB₄O₇:Sm, while the green phosphor may alsobe SrGa₂S₄:Eu.

The diffusing agent 3, which performs the function of scattering ordiffusing light to make the light uniform, is divided mainly into atransparent diffusing agent and a white diffusing agent. Examples of atransparent diffusing agent include organic transparent diffusing agentssuch as acrylic resin, styrene resin, and silicone resin, etc., andinorganic transparent diffusing agents such as synthetic silica, glassbeads, and diamond, etc. Typical examples of the white diffusing agentinclude silicon dioxide (SiO₂), titanium dioxide (TiO₂), zinc oxide(ZnO), barium sulfate (BASO₄), calcium sulfate (CaSO₄), magnesiumcarbonate (MgCO₃), aluminum hydroxide (Al(OH)₃), and inorganic oxidescontaining clay, etc.

The size and concentration of the diffusing agent 3 material are majorfactors that determine the degree of scattering of light emitted from alight source. If the diffusing agent 3 is too small in size, the lightdiffusion efficiency may be lowered, while too much of the diffusingagent 3 may lower the light transmissivity. In an embodiment of thepresent invention, the best results were obtained with sizes of SiO₂from 5 to 7 μm. Also, desirable results for light diffusion andtransmissivity were obtained when the concentration of the diffusingagent 3 was 13%.

As in the case of the diffusing agent 3, the size of the phosphor 1material is also restricted. A size of 5˜7 μm may be suitable for thephosphor 1, as an excessively small size reduces the light excitationefficiency, while an excessively large size lowers the lighttransmissivity and uniformity of the thin film.

However, the diffusing agent 3 is not of critical importance, as it ispossible to sufficiently diffuse light by deforming the surfaces of thephotoluminescent sheet 10.

Protective Film 4

A colorless transparent synthetic resin, which has high lighttransmissivity, may be used for the protective film 4 in an embodimentof the invention, which includes, but is not limited to, polyethyleneterephthalate (PET), polyethylene naphthalate, acrylic resin,polycarbonate, and polystyrene, etc. Among these, a polyethyleneterephthalate (PET) film is superior in terms of transparency, and hashigh strength and flexibility. When heat resistance and chemicalresistance are required, it may be preferable to use polycarbonate forthe protective film 4. Preferably, a film having a thickness of 5˜50 μmmay be used for the protective film 4. This is because a film having athickness of 5 μm or lower is difficult to handle, while a film having athickness of 50 μm or higher has lower light transmissivity.

Meanwhile, since a polymer screen used in screenprinting is low inmechanical strength, it may be preferable to use a stainless-steelscreen. The mesh size of the screen may be appropriately adjustedaccording to the printing thickness and grid size. In an embodiment ofthe invention, a screen having a mesh size of 50˜120 was used.

Other Materials

A curing agent cures liquid-phase silicone. While various types ofcuring agents may be used, the CF5010, CD7657, DC9800, LS4326, andDC2013 products from Dow Corning Corporation are generally used.

Also, one or more solutions selected from a dispersing agent fordispersing the phosphor 1 within the liquid silicone, asurface-defect-preventing agent, and a fluidity-enhancing additive maybe used as additives. When such additives are not used, the phosphor 1lumps together, to decrease the efficiency of the photoluminescent sheet10. Products from BYK Gmbh of Germany (BYK-333, BYK-306, BYK-310,BYK-w940, BYK-110, BYK-2001, BYK-410) are mainly used for the additives.Of course, any of a variety of products and substances may be used forthe above curing agent and additives according to usage.

In addition, an anti-precipitating agent, a binder, or antifoamingagent, etc., may be used for better mixing between the liquid siliconeresin and the phosphor 1 and optionally the diffusing agent 3, tofabricate a uniform sheet or to prevent the occurrence of bubbles.

The fabrication of a photoluminescent sheet 10, using the siliconeresin, additives, and phosphor 1 set forth above will be describedbelow, for the cases where a diffusing agent 3 is added and where adiffusing agent 3 is not added, for 100 parts by weight of the siliconeresin.

Tables 1 and 2 list the composition ratios for photoluminescent sheets;Table 1 for the case of adding a diffusing agent, and Table 2 for thecase of not using a diffusing agent.

TABLE 1 Composition Ratio of Photoluminescent Sheet with Diffusing AgentSilicone (parts by Curing Diffusing Green Yellow Red weight) AgentAdditive Agent Phosphor Phosphor Phosphor Luminance-Enhancing 100 0.05~50.1~15 5~15 0 1~90 0 Photoluminescent Sheet Luminance- and 100 0.05~50.1~15 5~15 1~30 0.1~60   1~30 Chromaticity- Enhancing PhotoluminescentSheet Chromaticity- 100 0.05~5 0.1~15 5~15 1~50 0 1~50 EnhancingPhotoluminescent Sheet

TABLE 2 Composition Ratio of Photoluminescent Sheet without DiffusingAgent Silicone (parts by Curing Green Yellow Red weight) Agent AdditivePhosphor Phosphor Phosphor Luminance-Enhancing 100 0.05~5 0.1~15 0 1~900 Photoluminescent Sheet Luminance- and 100 0.05~5 0.1~15 1~30 0.~60 1~30 Chromaticity- Enhancing Photoluminescent Sheet Chromaticity- 1000.05~5 0.1~15 1~65 0 1~65 Enhancing Photoluminescent Sheet

As in Tables 1 and 2, three main types of photoluminescent sheet may befabricated. Each of the photoluminescent sheets may be referred to,according to its characteristics, as a luminance-enhancingphotoluminescent sheet, a luminance- and chromaticity-enhancingphotoluminescent sheet, and a chromaticity-enhancing photoluminescentsheet.

The luminance-enhancing photoluminescent sheet uses only the yellowphosphor, among the various phosphors. Thus, when blue light isirradiated onto the photoluminescent sheet, the light that passes theyellow phosphor material displays a low peak at around 550 nm, which isthe wavelength region of yellow light, while the blue light that doesnot pass the yellow phosphor material displays a high peak at around itsoriginal 450 nm. This arrangement of wavelengths provides enhancedluminance. On the other hand, since white light requires a suitablecombination of red, green, and blue light, the light implemented by theluminance-enhancing photoluminescent sheet may be lacking inchromaticity.

However, since the light emitted from blue LED's generally does not havehigh luminance, it may be preferable to use a luminance-enhancingphotoluminescent sheet to ensure maximum luminance for light passing thephotoluminescent sheet.

When a diffusing agent is added, as in Table 1, the luminance-enhancingphotoluminescent sheet may be fabricated including 0.05˜5 parts byweight of the curing agent, 0.1˜15 parts by weight of the additive, 5˜15parts by weight of the diffusing agent, and 1˜90 parts by weight of theyellow phosphor, per 100 parts by weight of the silicone resin. When thediffusing agent is not added, as in Table 2, the luminance-enhancingphotoluminescent sheet may be fabricated including 0.05˜5 parts byweight of the curing agent, 0.1˜15 parts by weight of the additive, and1˜90 parts by weight of the yellow phosphor, per 100 parts by weight ofthe silicone resin.

Meanwhile, the chromaticity-enhancing photoluminescent sheet is forimplementing white light. In particular, the chromaticity-enhancingphotoluminescent sheet is used in lighting devices, and this type ofsheet may be preferable in indoor spaces for everyday living, in orderto reduce fatigue to the eyes.

The chromaticity-enhancing photoluminescent sheet uses a green phosphorand a red phosphor, from among the various phosphors. White light isimplemented when wavelengths of blue, green, and red colors are suitablycombined. Thus, when blue light is irradiated onto the photoluminescentsheet, the light that passes the red phosphor material displays a peakat around the wavelengths for red colors, and the light that passes thegreen phosphor material displays a peak at around the wavelengths forgreen colors, while the blue light that does not pass any of thephosphor materials displays a peak at around the wavelengths for bluecolors, such that the lights blend together to implement white light.

When a diffusing agent is added, as in Table 1, thechromaticity-enhancing photoluminescent sheet may be fabricatedincluding 0.05˜5 parts by weight of the curing agent, 0.1˜15 parts byweight of the additive, 5˜15 parts by weight of the diffusing agent,1˜50 parts by weight of the green phosphor, and 1˜50 parts by weight ofthe red phosphor, per 100 parts by weight of the silicone resin.

When the diffusing agent is not added, the chromaticity-enhancingphotoluminescent sheet may be fabricated including 0.05˜5 parts byweight of the curing agent, 0.1˜15 parts by weight of the additive, 1˜65parts by weight of the green phosphor, and 1˜65 parts by weight of thered phosphor, per 100 parts by weight of the silicone resin.

The luminance- and chromaticity-enhancing photoluminescent sheetcombines the advantages and disadvantages of the luminance-enhancingphotoluminescent sheet and the chromaticity-enhancing photoluminescentsheet. That is, the luminance- and chromaticity-enhancingphotoluminescent sheet has the advantage of increasing both theluminance and the chromaticity concurrently.

When a diffusing agent is added, the luminance- andchromaticity-enhancing photoluminescent sheet may be fabricatedincluding 0.05˜5 parts by weight of the curing agent, 0.1˜15 parts byweight of the additive, 5˜15 parts by weight of the diffusing agent,1˜30 parts by weight of the green phosphor, 0.1˜60 parts by weight ofthe yellow phosphor, and 1˜30 parts by weight of the red phosphor, per100 parts by weight of the silicone resin.

When the diffusing agent is not added, the luminance- andchromaticity-enhancing photoluminescent sheet may be fabricatedincluding 0.05˜5 parts by weight of the curing agent, 0.1˜15 parts byweight of the additive, 1˜30 parts by weight of the green phosphor,0.1˜60 parts by weight of the yellow phosphor, and 1˜30 parts by weightof the red phosphor, per 100 parts by weight of the silicone resin.

Analyzing the photoluminescent spectra of the three types ofphotoluminescent sheets set forth above may yield the graph shown inFIG. 3. As illustrated in FIG. 3, a peak is formed for theluminance-enhancing photoluminescent sheet across a broad range, whilehigh peaks are formed in the blue, red, and green wavelength regions forthe chromaticity-enhancing photoluminescent sheet.

Meanwhile, with respect to forming the three types of photoluminescentsheets set forth above, the reasons for limiting the composition rangesare explained below.

Effect of the Curing Agent

When the content of the curing agent is 0.05% or lower, there is almostno curing at all of the silicone resin after printing, and even whenthere is a curing effect, the curing time is increased to several hoursor several days, to cause a lack of productivity. On the other hand,when the content of the curing agent is 5% or higher, the curing occurstoo quickly, such that the curing may occur during the printing processfor fabricating the photoluminescent sheet.

When the curing occurs too early, the curing may occur while theprinting is being performed, such that the thickness of thephotoluminescent sheet is increased. This may cause serious processchanges of altered color coordinates, and may incur serious problems inthe reproduction of the fabrication process.

Effect of the Additives

One or more of a dispersing agent, a surface-defect-preventing agent,and a fluidity-enhancing additive may be mixed in for use as additives.When the amount of additives is below 0.1 weight %, there may be seriousseparation and aggregation between phosphor material after thephotoluminescent sheet is fabricated, to make it difficult to form auniform surface light source, and when the amount of additives is 15weight % or higher, reverse effects may occur, such as those listedbelow in Table 3.

TABLE 3 Types and Effects of Additives Reverse Effect when Type ofAdditive Product Name Effect Used Excessively Dispersing BYK110, 180,12001 prevents ag- flowing effect on Agent gregation, reduction printsurface in luster,color (non-uniformity in changes, color film surface)separation, and pre- cipitation, etc. Surface-Defect- BYK310, 333prevents color delayed curing, Preventing Agent separation, surfaceweakened adhesion, fluidity, crater and lowered surface effect, surfaceslip fluidity, when used foaming, etc. excessively, in the case ofBYK333 Fluidity-Enhancing BYK940, 410 prevents flow pre- flowing effecton Additive cipitation of surface print surface

As shown in Table 3, excessive use of the dispersing agent may create aflowing effect on the print surface, to cause non-uniformity in thesurface of the film (photoluminescent sheet). In the case of thesurface-defect-preventing agent, when the BYK333 is added in an excessamount, the curing may be delayed, the adhesion may be weakened, and thesurface fluidity may be lowered, while in the case of thefluidity-enhancing additive, an excess amount may cause a flowing effecton the print surface.

Effect of the Diffusing Agent

In the case where a diffusing agent is added in the sheet, the relationbetween the composition of the diffusing agent and luminance is as shownin Table 4 and the graph of FIG. 4. (Table 4 and the graph of FIG. 4 areresults of experiments on the luminance-enhancing photoluminescent sheetand the chromaticity-enhancing photoluminescent sheet.)

When the amount of the diffusing agent is 5 parts by weight or less per100 parts by weight of the silicone resin, there is almost no increasingeffect at all on luminance, and when the amount is 15 parts by weight ormore, there is a trend of decreasing luminance. Thus, a suitable amountmay be selected from the range of 5˜15 parts by weight.

TABLE 4 Diffusing Agent Concentration (per Luminance-EnhancingChromaticity-Enhancing 100 parts by weight PhotoluminescentPhotoluminescent of silicone resin) Sheet(cd/m) Sheet(cd/m²) 0 2830 19097 2831 1868 9 2898 1908 11 3021 1978 13 3001 2012 15 2871 1900

Effect of the Phosphor

As phosphors may have varying light emission and color coordinateproperties according to the manufacturer, it is difficult to establish afixed composition, and thus the phosphors have a wide range ofcompositions.

In the case of a luminance-enhancing photoluminescent sheet, there isalmost no excitation of the phosphor material with less than 1 part byweight per 100 parts by weight of the silicone resin, and as the lightfrom the blue LED light source occupies the major portion of theresulting light, the light is of a generally blue color. With 90 partsby weight or more, the color coordinates are beyond white and are moreof a yellow shade, and while the greater content of phosphors typicallylead to the higher luminance in the fabrication of phosphor sheets,there is almost no luminance increase for 90 parts by weight or more.

In the case of a luminance- and chromaticity-enhancing photoluminescentsheet, a composition of 1 part by weight of the green phosphor, 0.1parts by weight of the yellow phosphor, and 1 part by weight of the redphosphor or less, per 100 parts by weight of the silicone resin, causesalmost no excitation of the phosphor material at all, so that the lightis of a generally blue color, and there is almost no luminance increasefor 30 parts by weight of the green phosphor, 60 parts by weight of theyellow phosphor, and 30 parts by weight of the red phosphor or more.

In the case of a chromaticity-enhancing photoluminescent sheet, there isalmost no excitation of the phosphor material with less than 1 part byweight of the green phosphor and 1 part by weight of the red phosphorper 100 parts by weight of the silicone resin, so that the light is of agenerally blue color, and there is almost no luminance increase for 50parts by weight of the green phosphor and 50 parts by weight of the redphosphor or more. When a diffusing agent is not used, the green phosphormay be used up to 65 parts by weight, and the red phosphor may be usedup to 65 parts by weight.

A method of fabricating the photoluminescent sheet considering the rangeof composition ratios set forth above will be described below. FIG. 5 isa flowchart illustrating a method of fabricating a photoluminescentsheet according to a fourth disclosed embodiment of the presentinvention, and FIG. 6 is a schematic diagram illustrating a method offabricating a photoluminescent sheet according to the fourth disclosedembodiment of the present invention. In FIG. 6 are illustrated aprotective film 4, a photoluminescent sheet 10, and silicone liquid 20.

Method of Fabrication

The curing agent, the phosphor, and optionally the diffusing agent aremixed and stirred into the silicone resin of a gel form, and theviscosity is adjusted by means of silicone oil, etc., at which thesilicone liquid is fabricated. Afterwards, it is printed onto theprotective film by screenprinting, slit coating, or roll coating, etc.,and dry-cured to fabricate the photoluminescent sheet 10. While thephotoluminescent sheet 10 may also be used after removing the protectivefilm 4, it is generally preferable to leave the protective film 4attached, for protection.

Examining the fabrication method in more detail,

A liquid silicone resin was fabricated by sequentially adding thesilicone resin, and 0.5 parts by weight of the curing agent and 2 partsby weight of the curing accelerator per 100 parts by weight of thesilicone resin. For the liquid silicone resin fabricated in the mannerset forth above, 13 parts by weight of the phosphor and 13 parts byweight of SiO₂ (5˜7 μm in diameter) as the diffusing agent were mixedinto the liquid silicone resin and stirred using a revolving andorbiting stirrer to fabricate a silicone liquid 20. Next, the mixedsilicone liquid described above was coated, using screenprinting, onto aprotective film 4 (made of polyethylene) having a double-layerstructure, of which the first layer has a thickness of 10˜25 μm and thesecond layer has a thickness of 20˜100 μm, as the printing surface.After curing in an infrared drier at 120° C., the protective film 4 wasseparated, to fabricate a photoluminescent sheet based on an embodimentof the invention.

However, instead of separating the protective film 4, another layer ofprotective film 4 may further be stacked. This may increase the heat-and humidity-resistance of the photoluminescent sheet 10.

The photoluminescent sheet according to an embodiment of the inventionhas superior flexibility, such that it only bends and does not break.FIG. 7 is a photograph (without the protective film 4) of thephotoluminescent sheet according to the fourth disclosed embodiment ofthe present invention, which shows how the photoluminescent sheet has nocracks on the surface.

In prior art, a film was produced from thermoplastic resin by extrudingand pulling, without a protective film. Reliability testing performed onsuch conventional thermoplastic resin in a high temperature (80˜85° C.)and high humidity (80˜85%) atmosphere provides the results shown in thephotograph of FIG. 8. As in the photograph, the surface phosphors wereseparated and lost, while the phosphor material itself was alsodeteriorated, such that there was a serious reduction in luminance.

However, with the present embodiment, silicone resin was used, which isa kind of thermosetting resin, the results of which are no losses ordeterioration of surface phosphors, as seen in the photograph of FIG. 9,and thus almost no reduction in luminance.

Moreover, when a protective film 4 was stacked, there were nodeterioration or reduction in luminance even in a high temperature andhigh humidity environment.

Meanwhile, when a sheet of a different type from the photoluminescentsheet is stacked, the sheets adhere together to cause a wettingphenomenon. Therefore, there may be a need to separate each of thesheets by a minute distance. An embodiment will be described below whichprovides an improvement in this matter.

FIG. 10 is a cross-sectional view of a photoluminescent sheet accordingto a fifth disclosed embodiment of the present invention, and FIG. 11 isa photograph of the photoluminescent sheet having minute balls attached,according to the fifth disclosed embodiment of the present invention. InFIG. 10 are illustrated a phosphor 1, a matrix resin layer 2, adiffusing agent 3, protective films 4, minute balls 5, attachment layers6, and a photoluminescent sheet 10.

The fifth disclosed embodiment of the invention is characterized byattaching minute balls 5 on the surfaces of the photoluminescent sheet10. When the minute balls 5 are evenly dispersed and attached on thesurfaces of the photoluminescent sheet 10, the wetting phenomenon causedby close adhesion of the surfaces may be avoided, even when differenttypes of sheets are placed on the upper and lower surfaces.

Preferably, the minute balls 5 may also be made from resin, and it maybe preferable to use a transparent material, so as not to lower theluminance. While the minute balls 5 may be attached directly on thesurfaces of the photoluminescent sheet 10, coating an attachment layer 6on the outer surface may prevent the minute balls 5 from becomingdetached and may allow a stable manner of attachment.

FIG. 11 is a photograph seen from above of the fifth disclosedembodiment of the invention, where minute balls are dispersed over andattached onto the surface of the photoluminescent sheet.

FIG. 12 is a cross-sectional view of a photoluminescent sheet accordingto a sixth disclosed embodiment of the present invention. In FIG. 12 areillustrated a phosphor 1, a matrix resin layer 2, a diffusing agent 3,protective films 4, and a photoluminescent sheet 10.

In the sixth disclosed embodiment, the surfaces of the protective film 4have been treated to have roughness. This is in order to effectivelydiffuse light. That is, light incident on the matrix resin layer 2passes a protective film 4 twice, where the roughness of the protectivefilms 4 allows the paths of the light to be widely dispersed. Thus, thisphotoluminescent sheet 10 may be used without a diffusion agent 3. Inaddition, the rough surface of the protective film 4 also prevents thewetting phenomenon caused by close adhesion of the surfaces, when adifferent type of sheet is placed on the outer surfaces.

FIG. 13 is a cross-sectional view of a photoluminescent sheet accordingto a seventh disclosed embodiment of the present invention. A phosphor1, a matrix resin layer 2, a diffusing agent 3, protective films 4,minute balls 5, and a photoluminescent sheet 10 are illustrated. In thisembodiment, minute balls 5 are attached on the outer surfaces of theprotective films 4, which are made to have roughness, as in the sixthdisclosed embodiment of FIG. 12, to enhance the function of preventingwetting.

While the present invention was described in detail with reference tothe particular embodiments, the embodiments are merely for the purposeof illustration, and are not to limit the invention. It is to beappreciated by those skilled in the art that various embodiments may beconceived without departing from the spirit of the present invention.

INDUSTRIAL APPLICABILITY

According to aspects of the invention set forth above, aphotoluminescent sheet is provided which can reliably implement whitelight from the light of blue LED's.

1. A photoluminescent sheet comprising: a matrix resin layer ofthermosetting resin; a phosphor, included in the matrix resin layer,capable of converting a wavelength of light emitted from a blue LED; acuring agent, included in the matrix resin layer, capable of curingliquid thermosetting resin; and an additive, included in the matrixresin layer, capable of dispersing the phosphor uniformly within thematrix resin layer.
 2. The photoluminescent sheet of claim 1, whereinthe thermosetting resin is silicone resin, and the phosphor is a yellowphosphor, the photoluminescent sheet comprising 0.05˜5 parts by weightof the curing agent, 0.1˜15 parts by weight of the additive, and 1˜90parts by weight of the yellow phosphor, per 100 parts by weight of thesilicone resin.
 3. The photoluminescent sheet of claim 1, wherein thethermosetting resin is silicone resin, and the phosphor comprises agreen phosphor, a yellow phosphor, and a red phosphor, thephotoluminescent sheet comprising 0.05˜5 parts by weight of the curingagent, 0.1˜15 parts by weight of the additive, 1˜30 parts by weight ofthe green phosphor, 0.1˜60 parts by weight of the yellow phosphor, and1˜30 parts by weight of the red phosphor, per 100 parts by weight of thesilicone resin.
 4. The photoluminescent sheet of claim 1, wherein thethermosetting resin is silicone resin, and the phosphor comprises agreen phosphor and a red phosphor, the photoluminescent sheet comprising0.05˜5 parts by weight of the curing agent, 0.1˜15 parts by weight ofthe additive, 1˜65 parts by weight of the green phosphor, and 1˜65 partsby weight of the red phosphor, per 100 parts by weight of the siliconeresin.
 5. The photoluminescent sheet of claim 1, wherein thethermosetting resin is silicone resin, a diffusing agent capable ofrefracting light is added to the silicone resin, and the phosphorcomprises a yellow phosphor, the photoluminescent sheet comprising0.05˜5 parts by weight of the curing agent, 0.1˜15 parts by weight ofthe additive, 5˜15 parts by weight of the diffusing agent, and 1˜90parts by weight of the yellow phosphor, per 100 parts by weight of thesilicone resin.
 6. The photoluminescent sheet of claim 1, wherein thethermosetting resin is silicone resin, a diffusing agent capable ofrefracting light is added to the silicone resin, and the phosphorcomprises a green phosphor, a yellow phosphor, and a red phosphor, thephotoluminescent sheet comprising 0.05˜5 parts by weight of the curingagent, 0.1˜15 parts by weight of the additive, 5˜15 parts by weight ofthe diffusing agent, 1˜30 parts by weight of the green phosphor, 0.1˜60parts by weight of the yellow phosphor, and 1˜30 parts by weight of thered phosphor, per 100 parts by weight of the silicone resin.
 7. Thephotoluminescent sheet of claim 1, wherein the thermosetting resin issilicone resin, a diffusing agent capable of refracting light is addedto the silicone resin, and the phosphor comprises a green phosphor and ared phosphor, the photoluminescent sheet comprising 0.05˜5 parts byweight of the curing agent, 0.1˜15 parts by weight of the additive, 5˜15parts by weight of the diffusing agent, 1˜50 parts by weight of thegreen phosphor, and 1˜50 parts by weight of the red phosphor, per 100parts by weight of the silicone resin.
 8. The photoluminescent sheet ofclaim 1, wherein a protective film is attached to a surface of thematrix resin layer.
 9. The photoluminescent sheet of claim 8, whereinminute balls for preventing wetting are attached to a surface of theprotective film.
 10. The photoluminescent sheet of claim 8, wherein asurface of the protective film has roughness.